A TV tech told me the other day I could extend my recording hours on our Zinwell zmt-640pvr by simply buying an external wd hard drive and plugging it in to the back of the unit, if so, it would be a quick fix to gobbling up all our internal hard drive with recording things for the kids.  Has anyone done this,  and is it true.  I have a suspicion that you may be only to play things from the external hard drive but not store things on it from the unit itself.